The invention relates to processing systems for ores and the like, and more particularly to such systems employing a rotary kiln for roasting or otherwise heat-treating a charge of the ore in a controllable atmosphere having an elevated temperature and pressure. Rotary kilns which are presently employed in such systems exhibit a main cylindrical processing zone which is coupled to a charge-inlet zone and a charge-outlet zone. In order to optimize the conditions of treatment of the introduced charge in the main processing zone by a suitably established reactive atmosphere (e.g., which may be introduced directly or liberated from a solid reagent such as coal or coke), the temperature-time reaction curve of the ore treated in the processing zone must be held constant. This, in turn, requires essentially invariant atmospheric conditions within such zone.
Unfortunately, in present rotary kiln designs, the reaction atmosphere in the main processing zone cannot effectively be maintained constant because of the leakage of the reaction gas out of, and the seeping of oxygen-filled outside air into, the processing zone via the interface between such zone and the charge-introducing port of the kiln. The resulting contamination of the reaction atmosphere within the processing zone adversely affects the quality of the treated charge and severely reduces the kiln efficiency. Because of such problems, the rotary kiln cannot even be employed for certain types of heat-treatment, i.e., segregation roasting.
An additional impediment in such systems to the maintenance of a constant reactive atmosphere is the fact that the associated facilities for withdrawing the spent reactive gases from the main processing zone do not, in general, serve to maintain a desired value of superatmospheric pressure within the processing zone once such pressure is established by the zone heating.